The present invention relates to photosensitive microcapsules which are useful in forming polychromatic or full color images using the imaging processes described in U.S. Pat. Nos. 4,399,209 and 4,440,846 to The Mead Corporation. More particularly, the present invention relates to photosensitive microcapsules containing a photosensitive composition in which a radiation absorber is associated with the microcapsules. The radiation absorber reduces the sensitivity of the microcapsules at certain wavelengths such that a set of microcapsules containing the color formers necessary for full color imaging can be designed in which the microcapsules have sufficiently distinct spectral sensitivities that they can be discriminately hardened using exposures at distinctly different radiation wavelengths.
U.S. patent application Ser. No. 339,917 filed Jan. 18, 1982, by The Mead Corporation describes a photosensitive material useful in full color imaging comprising a support having on the surface thereof microcapsules which individually contain cyan, magenta and yellow color formers and photosensitive compositions having distinctly different sensitivities. A uniform mixture of the microcapsules is distributed over the surface of the support. Images are formed by separating the red, green and blue components of the image to be reproduced and translating these components into different wavelengths of actinic radiation to which the photosensitive compositions are distinctly sensitive. The photosensitive material is image-wise exposed to the translated radiation and thereafter it is subjected to a uniform rupturing force, such as pressure, which causes the microcapsules in the underexposed and unexposed areas to rupture and release the color formers. The color formers then react with a developer material which is contained on the same or a different support and produce a full color image.
The spectral sensitivity of photosensitive microcapsules is principally a function of the photoinitiator used in the encapsulated photosensitive composition. In order to design photosensitive microcapsules useful in full color imaging having distinctly different spectral sensitivities, photoinitiators must be designed or selected which have mutually exclusive sensitivities in at least three distinct wavelength regions. That is, the photoinitiator used in microcapsules containing a cyan color former must be substantially more sensitive in a wavelength region in which the photoinitiators used in the microcapsules associated with the magenta and yellow color formers are substantially less sensitive or insensitive. Likewise, the photoinitiator used in the microcapsules containing the cyan color former must be substantially less sensitive and ideally insensitive in a wavelength region in which the photoinitiators used in the microcapsules containing the magenta and yellow color formers are preferentially sensitive. The same considerations govern the selection of the initiators associated with the microcapsules containing the yellow and magenta color formers.
The selection and/or design of microcapsules having mutually exclusive sensitivity characteristics as described above is simplified by associating a radiation absorber with the microcapsules in accordance with the present invention.